1 files changed, 91 insertions, 0 deletions
diff --git a/compiler/rustc_mir_transform/src/check_inline.rs b/compiler/rustc_mir_transform/src/check_inline.rs
new file mode 100644
index 00000000000..497f4a660ea
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/check_inline.rs
@@ -0,0 +1,91 @@
+//! Check that a body annotated with `#[rustc_force_inline]` will not fail to inline based on its
+//! definition alone (irrespective of any specific caller).
+
+use rustc_attr_parsing::InlineAttr;
+use rustc_hir::def_id::DefId;
+use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
+use rustc_middle::mir::{Body, TerminatorKind};
+use rustc_middle::ty;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::sym;
+
+use crate::pass_manager::MirLint;
+
+pub(super) struct CheckForceInline;
+
+impl<'tcx> MirLint<'tcx> for CheckForceInline {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
+        let def_id = body.source.def_id();
+        if !tcx.hir().body_owner_kind(def_id).is_fn_or_closure() || !def_id.is_local() {
+            return;
+        }
+        let InlineAttr::Force { attr_span, .. } = tcx.codegen_fn_attrs(def_id).inline else {
+            return;
+        };
+
+        if let Err(reason) =
+            is_inline_valid_on_fn(tcx, def_id).and_then(|_| is_inline_valid_on_body(tcx, body))
+        {
+            tcx.dcx().emit_err(crate::errors::InvalidForceInline {
+                attr_span,
+                callee_span: tcx.def_span(def_id),
+                callee: tcx.def_path_str(def_id),
+                reason,
+            });
+        }
+    }
+}
+
+pub(super) fn is_inline_valid_on_fn<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    def_id: DefId,
+) -> Result<(), &'static str> {
+    let codegen_attrs = tcx.codegen_fn_attrs(def_id);
+    if tcx.has_attr(def_id, sym::rustc_no_mir_inline) {
+        return Err("#[rustc_no_mir_inline]");
+    }
+
+    // FIXME(#127234): Coverage instrumentation currently doesn't handle inlined
+    // MIR correctly when Modified Condition/Decision Coverage is enabled.
+    if tcx.sess.instrument_coverage_mcdc() {
+        return Err("incompatible with MC/DC coverage");
+    }
+
+    let ty = tcx.type_of(def_id);
+    if match ty.instantiate_identity().kind() {
+        ty::FnDef(..) => tcx.fn_sig(def_id).instantiate_identity().c_variadic(),
+        ty::Closure(_, args) => args.as_closure().sig().c_variadic(),
+        _ => false,
+    } {
+        return Err("C variadic");
+    }
+
+    if codegen_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
+        return Err("cold");
+    }
+
+    // Intrinsic fallback bodies are automatically made cross-crate inlineable,
+    // but at this stage we don't know whether codegen knows the intrinsic,
+    // so just conservatively don't inline it. This also ensures that we do not
+    // accidentally inline the body of an intrinsic that *must* be overridden.
+    if tcx.has_attr(def_id, sym::rustc_intrinsic) {
+        return Err("callee is an intrinsic");
+    }
+
+    Ok(())
+}
+
+pub(super) fn is_inline_valid_on_body<'tcx>(
+    _: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+) -> Result<(), &'static str> {
+    if body
+        .basic_blocks
+        .iter()
+        .any(|bb| matches!(bb.terminator().kind, TerminatorKind::TailCall { .. }))
+    {
+        return Err("can't inline functions with tail calls");
+    }
+
+    Ok(())
+}